1. Field of the Invention
This invention broadly concerns aqueous dispersions and methods for controlling sulfide deposits, especially downhole metal sulfide deposits associated with oil and/or gas wells. When introduced into a well, the aqueous dispersion reacts with the metal sulfide deposits and sequesters the metal ion. Through this process, downhole metal sulfide scaling is controlled.
2. Description of the Prior Art
The presence of downhole metal sulfide deposits, more specifically iron and zinc sulfides, is a serious problem encountered in certain oil well operations. These metal sulfides form a corrosive scale on the downhole equipment. If left untreated, the scale may corrode and destroy downhole equipment and lead to a stoppage in production.
The leading method of treating wells characterized by downhole metal sulfide deposits is through the use of acrylic aldehyde, also commonly known as acrolein. The acrolein data sheet distributed by the Agency for Toxic Substances and Disease Registry, Atlanta, Ga. is hereby incorporated by reference. Acrolein possesses numerous undesirable and hazardous qualities. Acrolein is an extremely reactive chemical and is sensitive to heat and light. It polymerizes violently, especially on contact with strong acids or bases. It is incompatible with amines, sulfur dioxide, metal salts and oxidants. It is for this reason that when treating a well with acrolein, the acrolein is pushed downhole with nitrogen gas.
Acrolein is poisonous to humans and must be handled with extreme caution. Acrolein fumes can cause severe eye and skin irritation and prolonged exposure can even result in death. Therefore protective clothing and a self-contained breathing apparatus are recommended equipment when working with acrolein.
In view of the foregoing problems associated with acrolein, there is a need in the art for a composition that effectively controls downhole metal sulfide deposits and is less volatile and less toxic than acrolein.
The present invention overcomes the problems associated with the use of acrolein, while at the same time provides effective compositions and methods for treating downhole metal sulfide deposits.
Compositions of the present invention are aqueous dispersions which generally comprise a thioacid, an amine salt, and a diphosphonic acid. It is preferable that the thioacid be selected from the group of acids having the formula Rxe2x80x94SH, where R is a C2-C12 carboxylic acid moiety, and more preferably thioglycolic acid. The amine salt may comprise any primary, secondary, tertiary, or quaternary amine salt. Preferably the amine salt is quaternary and comprises an amine halide salt having the formula 
where R2 is an aryl or aliphatic C1-C12 hydrocarbon moiety, and Xxe2x88x92 is a halide anion, preferably a chloride anion. Most preferably, R2 is a benzyl moiety. It is most preferable that the salt comprise benzyl trimethyl quaternary ammonium chloride.
Preferably the diphosphonic acid will have the general formula 
where R3 is a C1-C12 alkyl moiety. Most preferably, the diphosphonic acid will comprise hydroxyethylidene diphosphonic acid (HEDP).
The thioacid is generally present at a level of from about 5-50% by weight, more preferably from about 10-35% by weight, and most preferably from about 20-30% by weight. All weight percentages disclosed herein, unless otherwise specified, are based upon the weight of the dispersion being 100%. The amine salt is generally present at a level of from about 1-25% by weight, more preferably from about 5-20% by weight, and most preferably from about 5-15% by weight. The quantity of diphosponic acid present in the dispersion ranges from about 1-25% by weight, more preferably from about 5-20% by weight, and most preferably from about 5-15% by weight.
The aqueous dispersion may also comprise various other inert compounds which impart desirable properties to the dispersion. Ethylene glycol is an example of such additional component which acts as a freezing point depressant. The amount of ethylene glycol to be used will depend upon the conditions under which the dispersion is being stored or used. However, it is preferable that the dispersion comprise between about 5-50% by weight ethylene glycol, more preferably between about 20-50% by weight, and most preferably between about 30-50% by weight.
The dispersion generally will comprise between about 5-50% by weight water, more preferably between about 10-40% by weight, and most preferably between about 10-20% by weight. Preferably, the dispersion will have a pH between about 1-5.
A preferred embodiment of the aqueous dispersion will comprise about 25% by weight thioglycolic acid, about 10% by weight of benzyl trimethyl quaternary ammonium chloride, about 10% by weight of HEDP, about 35% by weight water, and about 20% by weight ethylene glycol.
One preferred use of an aqueous dispersion according to the invention is in the treatment of systems, such as oil and/or gas wells, characterized by the presence of metal sulfides. These methods generally comprise the steps of providing an aqueous dispersion comprising a thioacid, an amine salt, and a diphosphonic acid, and introducing the dispersion into the system. In general, the aqueous dispersion for use with the methods of this invention may be any dispersion described above.
Methods of treating systems characterized by the presence of metal sulfides are useful in treating oil and/or gas wells characterized by the presence of downhole iron sulfide and zinc sulfide. During treatment, the aqueous dispersion will react with these downhole metal sulfide deposits thereby protecting the downhole equipment from the destructive effects of the scale.
It is also within the scope of the invention to provide a sulfide treatment wherein individual quantities of thioacid, amine salt and diphosphonic acid are separately introduced into the system. Preferred thioacid, amine salt, and diphosphonic acid ingredients are the same as those previously discussed.
It is preferable that the individual quantity of thioacid introduced into the system be between about 5-50% by weight, more preferably between 10-35% by weight, and most preferably between 20-30% by weight based on the total weight of all thioacid, amine salt, and diphosphonic acid introduced into the system. It is preferable that the individual quantity of amine salt introduced into the system be between about 1-25% by weight, more preferably between 5-20% by weight, and most preferably between 5-15% by weight based on the total weight of all thioacid, amine salt, and diphosphonic acid introduced into the system. Finally, it is preferable that the individual quantity of diphosphonic acid introduced into the system be between about 1-25% by weight, more preferably between 5-20% by weight, and most preferably between 5-15% by weight based on the total weight of all thioacid, amine salt, and diphosphonic acid introduced into the system.
It is also possible to introduce into the system individual quantities of inert compounds. For example, ethylene glycol may be introduced into the system at a level of between 5-50% by weight, more preferably between 20-50% by weight, and most preferably between 30-50% by weight based on the total weight of all thioacid, amine salt, diphosphonic acid, and ethylene glycol introduced into the system. Individual quantities of water may also be introduced into the system at a level of between 5-50% by weight, more preferably between 10-40% by weight, and most preferably between 10-20% by weight based on the total weight of all thioacid, amine salt, diphosphonic acid, and water introduced into the system.
The individual quantities of the above-named components may be particularly useful for introduction into systems such as oil and/or gas wells for the treatment of downhole iron sulfide and zinc sulfide deposits. When introduced into the well, the thioacid, amine salt, and phosphonic acid act upon the downhole metal sulfide deposits thereby sequestering the metal ion.